My next door neighbor finally let her sons have a betta but only if they would put it in a jar...........(yikes!). He is lethargic and unhappy...............The kids do a great job of keeping the jar (over 1 gallon) clean with regular water changes, and there are lots of plant roots in there to keep him happy and squeezed in tight, and they feed him the right kinds of foods....but he is cold. (They keep the temp around 63 F to keep the gas bill down). How could these kids keep the Betta warm??? I cannot save him as they really do love him and I have no room. They don't understand what the big deal is......and if I took him they would just get another. I am not sure that a regular aquarium heater would fit in there, so what do you all think? Please help me, I can't stand knowing he is cold.